First of all, hello everybody! I am new in here and would love to join the wonderful community of Cardano.

Sadly, I am having an issue with accessing my coins. I am using the linux version of Daedalus (still in beta, I know) and I don’t have any machine with non-linux operating system. Recently I start having an issue with Daedalus being stuck at cca 99.23% when syncing blockchain. This value stays there for hours without moving (it just moves down since the blockchain grows, obviously).

I know that there are some tricks how to fix this on Windows (deleting some tmp directory and syncing again). Is there something like this available for Linux?

I also tried using my 12-word passphrase to recover the wallet in Yoroi but it only says it is invalid (Yoroi and Daedalus passphrases are not compatible, it seems). So my question is, what should I do to access my coins?

Network users should download a new version of the Daedalus wallet after IOHK made a system update today.
The update this weekend contains a minor software update. This follows a patch issued earlier this week to remedy abuse of large addresses, which could have been used to add inappropriate images and data to the blockchain.
The network is running well and at no point were user funds affected.
To make the update, users are required to download the latest version of the Daedalus wallet.
You…

I’m not sure what the status of the Linux version is, but you could try making sure it’s updated to the latest version and see if that fixes the issue.

You can’t put your 12 word Daedalus phrase straight into Yoroi. You need to create a new Yoroi wallet with a 15 word phrase, then click the Daedalus logo at the top right of Yoroi and choose to import the funds from Daedalus. This transfers all the ADA out of your Daedalus wallet into your new Yoroi wallet.
Edit: Here’s a video on how to import Daedalus to Yoroi